The present invention relates to a front and rear wheel load distribution control unit for a coupled vehicle.
A coupled vehicle, for example, an articulated dump truck as shown in FIG. 5 includes a vertical shaft for articulation at a coupling element between a front vehicle body 1 having a driver""s cab and a rear vehicle body 3 having a dump body 5 capable of dumping earth, and it also has a horizontal shaft in a longitudinal direction (for example, refer to Japanese Patent Application Laid-open No. 9-254831). The dump truck is allowed to turn around the horizontal shaft, specifically, it is capable of oscillating so as to have improved adhesion of front and rear wheels during traveling and excellent stability of a vehicle body.
The front vehicle body 1 having front wheels 2 and a rear vehicle body 3 having rear wheels 4 are coupled by means of a coupling device 10 being an oscillation device. The front vehicle body 1 is provided with the driver""s cab, and the rear vehicle body 3 is mounted with the dump body 5 loaded with earth and sand or the like. During earth dumping, the dump body 5 is dumped rearward by a dump cylinder not illustrated to discharge earth as shown by the two-dot chain line.
FIG. 6 is an explanatory view of the coupling device 10 in FIG. 5. One end of a coupling member 11 is attached to the front vehicle body 1 so as to be rotatable around a horizontal axis Xxe2x80x94X in the longitudinal direction as shown by the arrow, that is, so as to be able to oscillate. A rear vehicle body frame 7 is attached to the other end of the coupling member 11 so as to be rotatable around a vertical axis Yxe2x80x94Y.
FIG. 7 is a plan view of the articulated dump truck. When the dump truck turns during traveling, the front vehicle body 1 is turned around the vertical axis Yxe2x80x94Y (See FIG. 6) to the right (or left) as shown by the two-dot chain line as shown in FIG. 7 to make a turn.
The above articulated dump truck has an all-wheel-drive unit which drives all wheels as shown in FIG. 8. The drive unit is provided with an inter-axle differential 53 for absorbing rotation differentials between the front wheels 2 and the rear wheels 4, and an inter-axle differential lock 71 for locking the inter-axle differential 53 so as to allow the front wheels 2 and the rear wheels 4 to drive without a rotation differential in order to prevent the front wheels 2 or the rear wheels 4 from skidding on a soft ground. The drive unit is also provided with a front differential 54 and rear differentials 56 and 58 for absorbing the rotation differentials between left and right wheels, and differential locks 72, 73, and 74 for locking the front differential 54, and the rear differentials 56 and 58 so as to allow the left and right wheels to drive without rotation differentials in order to prevent either left wheel or right wheel from skidding on a soft ground.
Next, the details of the drive unit will be explained. An output shaft of an engine 50 connects to an input shaft of a torque converter 51a, and an output shaft of the torque converter 51a connects to an input shaft of a transmission 51. An output shaft of the transmission 51 connects to a transfer device 52 for distributively transferring output power to a front axle 91, and a front rear axle 92 and a back rear axle 93 which are rear axles. The transfer device 52 connects to the front axle 91 via a front propeller shaft 95 in front and connects to the front rear axle 92 via a first rear propeller shaft 96 and a second rear propeller shaft 94 in the rear. By this connection, the output power of the engine 50 is distributively transferred to the front wheels 2 and the rear wheels 4 finally by gears inside the transfer device 52. A gear box 55 and a gear box 57 respectively connect to the front rear axle 92 and the back rear axle 93 via a back rear propeller shaft 97.
The transfer device 52 is provided with the inter-axle differential 53 as a differential in order to transfer input power, dividing it into output powers to the front wheels 2 and the rear wheels 4 and to absorb the rotation differential between the front wheel 2 and the rear wheel 4. The transfer device 52 is provided with the inter-axle differential lock 71 for fixing the inter-axle differential 53 to bring the differential to a non-operation state.
The front side of the inter-axle differential 53 connects to the front differential 54 being a differential. The front differential 54 is provided with the front differential lock 72 for fixing the front differential 54 to bring the differential to a non-operation state. An output shaft of the front differential 54 connects to left and right final reduction gears 84, to which the front wheels 2 are mounted. The front axle 91 is provided with front brakes 81 for braking the front wheels 2.
The rear side of the inter-axle differential 53 connects to the front rear differential 56 being a differential via the gear box 55 of the front rear axle 92 being one of the rear axles. The front rear differential 56 is provided with the front rear differential lock 73 for fixing the front rear differential 56 to bring the differential to a non-operation state. An output shaft of the front rear differential 56 connects to left and right final reduction gears 85, to which the rear wheels 4 are mounted. The front rear axle 92 is provided with front rear brakes 82 for braking the rear wheels 4.
The front rear axle 92 connects to the back rear differential 58 being a differential of the back rear axle 93 being the other one of the rear axles via the gear boxes 55 and 57. The back rear differential 58 is provided with the back rear differential lock 74 for fixing the back rear differential 58 to bring the differential to a non-operation state. An output shaft of the back rear differential 58 connects to left and right final reduction gears 86, to which the rear wheels 4 are mounted. The back rear axle 93 is provided with back rear brakes 83 for braking the rear wheels 4.
The inter-axle differential lock 71, the front differential lock 72, the front rear differential lock 73, and the back rear differential lock 74, which bring the respective differentials to a non-operational state, fix gears 53a, 54a, 56a and 58a of the respective differentials, and pinion gears 53b, 54b, 56b and 58bon one side with such means as an oil hydraulic clutch. For example, an inter-axle differential lock clutch 71c of the inter-axle differential lock 71 is engaged by oil pressure to thereby fix the gear 53a and the pinion 53b. Consequently, when the inter-axle differential lock 71, the front differential lock 72, the front rear differential lock 73, and the back rear differential lock 74 are operated, the gears 53a, 54a, 56a and 58a of the respective differentials, the pinion gears 53b, 54b, 56b and 58bon one side, and pinion gears 53c, 54c, 56c and 58c on the other side are fixed, and thus no rotational differentials occur among them.
When the above articulated dump truck turns during traveling, as shown in FIG. 9, the front vehicle body 1 and the rear vehicle body 3 cross at the coupling element 10 to form a crossing angle of Sa. Generally, in an articulated dump truck as above, the rear vehicle body 3 is longer than the front vehicle body 1, and as a result, a distance L2 between the axis of the rear wheels 4 and the coupling element 10 is longer than a distance L1 between the axis of the front wheels 2 and the coupling element 10. Consequently, as for an outer turning radius from a center of turning Co, an outer turning radius R1 of the front wheel 2 is longer than an outer turning radius R3 of the rear wheel 4. On the other hand, as for an inner turning radius from a center of turning Co, an inner turning radius R2 of the front wheel 2 is longer than an inner turning radius R4 of the rear wheel 4.
Naturally, the outer turning radiuses R1 and R3 of the front wheel 2 and the rear wheel 4 are longer than inner turning radiuses R2 and R4. Accordingly, when the coupled vehicle turns during traveling, a rotational differential occurs between an outer wheel 2o and an inner wheel 2i of the front wheels 2, and rotational differentials also occur between an outer wheel 4o and an inner wheel 4i of the rear wheels 4. These rotational differentials are absorbed by the front differential 53 and the rear differential 56. The front propeller shaft 95 leading to the front axle 91 has a rotational speed corresponding to the average rotational speed of the outer wheel 2o and the inner wheel 2i of the front wheels 2. The first rear propeller shaft 96 leading to the rear axle 92 has a rotational speed corresponding to the average rotational speed of the outer wheel 4o and the inner wheel 4i of the rear wheels 4.
However, the outer turning radius R1 of the front wheel 2 is longer than the outer turning radius R3 of the rear wheel 4, and the inner turning radius R2 of the front wheel 2 is longer than the inner turning radius R4 of the rear wheel 4. Therefore, the rotational speed of the front propeller shaft 95 to the front axle 91 is higher than that of the first rear propeller shaft 96 to the rear axle 92. As a result, a rotational speed differential occurs between the front propeller shaft 95 and the first rear propeller shaft 96. The speed differential is absorbed by the inter axle differential 53. Consequently, even if the articulated dump truck, which is a coupled vehicle, turns during traveling, load caused by the rotational speed differential between the rotational speed of the front axle 91 and the rotational speed of the rear axle 92 does not occur to the drive unit, and thereby the dump truck can turn smoothly.
However, when the articulated dump truck being a coupled vehicle as above turns during traveling on a muddy ground or a wasteland, a disadvantage arises. Specifically, on turning as above, if the road surface is muddy and soft, the frictional force between the wheels and the road surface reduces, even if the dump truck travels with the rotational speed differentials between the front axle 91 and the rear axle 92 being absorbed by the inter-axle differential 53. As a result, even with an all-wheel drive, the driving force is not transferred to the road surface, and for example the front wheels skid with the front axle 91 idling. Then the front vehicle body 1 is pressed in a direction to which the rear vehicle body 3 faces by the driving force of the rear axle 92, and the vehicle does not turn. In addition, the driving force is used for idling the front axle 91, namely, for causing the front wheels 2 to skid, and thus it is wasted without being used for moving the vehicle.
In such a case, in order to prevent the front axle 91 or the rear axle 92 from idling, it is suitable to operate the interaxle differential lock 71 for locking the inter-axle differential 53 so that the front axle 91 and the rear axle 92 can drive without a rotational speed differential. However, it is troublesome for an operator to frequently perform operations of effecting and stopping the operation of the inter-axle differential lock 71. For this reason, the operator cannot concentrate attention on a turning operation of the vehicle on a wasteland or a muddy ground, which easily leads to unstable traveling, thus decreasing operability of the vehicle.
When the timing of operating the inter-axle differential lock 71 is not proper and it is operated on a hard ground, the differential mechanism does not work, and rotational speed differentials between the front axle 91 and the rear axle 92 are not absorbed. As a result, undue load is exerted on the drive unit, thereby reducing durability of the gears, bearings and propeller shafts of the driving unit, and the tires are forcibly rotated to skid, thereby increasing wear in the tires.
The present invention is made in view of the above disadvantages, and its object is to provide a front and rear wheel load distribution control unit for a coupled vehicle which provides excellent operability in driving the coupled vehicle, and which increases durability of a driving unit.
In order to attain the above object, a first aspect of a front and rear wheel load distribution control unit for a coupled vehicle according to the present invention is a front and rear wheel load distribution control unit for a coupled vehicle with a front vehicle and a rear vehicle being coupled, including an inter-axle differential lock between a front axle and a rear axle for eliminating a rotational differential between the front axle and the rear axle, and includes
a crossing angle detecting sensor for detecting a crossing angle of the front vehicle and the rear vehicle,
a front axle rotation sensor for detecting rotation of the front axle,
a rear axle rotation sensor for detecting rotation of the rear axle, and
control means for operating the inter-axle differential lock in response to a crossing angle signal from the crossing angle detecting sensor, a rotation signal from the front axle rotation sensor, and a rotation signal from the rear axle rotation sensor.
According to the above configuration, when the coupled vehicle turns during traveling on a wasteland such as a muddy ground, the inter-axle differential lock is automatically operated corresponding to the rotational speed differential between the front axle and the rear axle, and the crossing angle. As a result, the front axle and the rear axle do not idle, and the wheels do not skid, thus enabling the vehicle to smoothly turn. Consequently, the driving operability of the coupled vehicle is improved. Further, the inter-axle differential being a differential between the front and rear axles operates automatically and properly, and absorbs the rotational speed differentials between the front and rear axles, thus improving the durability of the drive unit of the coupled vehicle.
A second aspect of a front and rear wheel load distribution control unit for a coupled vehicle according to the present invention is a front and rear wheel load distribution control unit for a coupled vehicle with a front vehicle and a rear vehicle being coupled, including an inter-axle differential lock between a front axle and a rear axle for eliminating a rotational differential between the front axle and the rear axle, and includes
a crossing angle detecting sensor for detecting a crossing angle of the front vehicle and the rear vehicle,
a front axle rotation sensor for detecting rotation of the front axle,
a rear axle rotation sensor for detecting rotation of the rear axle, and
control means which obtain a rotational speed differential between the front axle and the rear axle and a theoretical value of the rotational speed differential between the front axle and the rear axle according to the crossing angle, or
which obtains a rotational speed ratio between the front axle and the rear axle and a theoretical value of the rotational speed ratio between the front axle and the rear axle according to the crossing angle,
based on a crossing angle signal from the crossing angle detecting sensor, a rotation signal from the front axle rotation sensor, and a rotation signal from the rear axle rotation sensor, and
which operates the inter-axle differential lock when an absolute value of the differential between the obtained rotational speed differential and the obtained theoretical value of the rotational speed differential exceeds a first rotational speed differential threshold value, or when an absolute value of the differential between the obtained rotational speed ratio and the obtained theoretical value of the rotational speed ratio exceeds a first rotational speed ratio threshold value.
According to the above configuration, when the coupled vehicle turns during traveling on a wasteland such as a muddy ground, i) the rotational speed differential between the front and rear axles, and the theoretical value of the rotational speed differential between the front and rear axles according to the crossing angle are obtained, or ii) the rotational speed ratio between the front and rear axles, and the theoretical value of the rotational speed ratio between the front and rear axles according to the crossing angle are obtained. As a result of obtaining them, if the absolute value of the differential between the rotational speed differential and the theoretical value of the rotational speed differential exceeds the first rotational speed differential threshold value, or if the absolute value of the differential between the rotational speed ratio and the theoretical value of the rotational speed ratio exceeds the first rotational speed ratio threshold value, the inter-axle differential lock is automatically operated. As a result, the front and rear axles do not idle, and the wheels do not skid, thus enabling the vehicle to smoothly turn. Consequently, driving operability of the coupled vehicle is improved. If the absolute value of the differential between the rotational speed differential and the theoretical value of the rotational speed differential does not exceed the first rotational speed differential threshold value, or if the absolute value of the differential between the rotational speed ratio and the theoretical value of the rotational speed ratio does not exceed the first rotational speed ratio threshold value, the inter-axle differential lock is not operated. As a result, the inter-axle differential being a differential between the front and rear axles is operated properly, and absorbs the rotational speed differential between the front and rear axles, thus improving the durability of the driving unit for the coupled vehicle.
In the control unit according to the present invention, the control means may further output a signal for reducing an engine speed of the coupled vehicle by a predetermined value when an absolute value of the differential between the obtained rotational speed differential and the obtained theoretical value of the rotational speed differential exceeds a second rotational speed differential threshold value which is larger than the first rotational speed differential threshold value, or when an absolute value of the differential between the obtained rotational speed ratio and the obtained theoretical value of the rotational speed ratio exceeds a second rotational speed ratio threshold value which is larger than the first rotational speed ratio threshold value.
According to the above configuration, the engine speed of the coupled vehicle is automatically reduced when the absolute value of the differential between the rotational speed differential and the theoretical value of the rotational speed differential exceeds the second rotational speed differential threshold value, or the absolute value of the differential between the rotational speed ratio and the theoretical value of the rotational speed ratio exceeds the second rotational speed ratio threshold value. As a result, the rotational speed of the front axle or the rear axle reduces, idling of the front axle or the rear axle is decreased by the degree of speed reduction, wear of the tires can be reduced, and the engine fuel consumption amount can be reduced.
Further, in the control unit according to the present invention, the control means may increase and decrease the magnitude of an operation signal for the inter-axle differential lock stepwise.
According to the above configuration, since the inter-axle differential lock is operated stepwise, shock occurring to the coupled vehicle can be reduced and hunting in which operation and non-operation of the inter-axle differential lock are repeated can be prevented. Consequently, smooth driving operability can be provided.